1. Field of the Invention
The present invention relates to an electro-optical device, typically an EL (electroluminescence) display device formed by a semiconductor element (an element using a semiconductor thin film) made on a substrate, and to electronic equipment (an electronic device) having the electro-optical device as a display (also referred to as a display portion).
2. Description of the Related Art
Techniques of forming a TFT on a substrate have been widely progressing in recent years, and developments of applications to an active matrix type display device are advancing. In particular, a TFT using a polysilicon film has a higher electric field effect mobility (also referred to as mobility) than a TFT using a conventional amorous silicon film, and high speed operation is therefore possible. As a result, it becomes possible to perform pixel control, conventionally performed by a driver circuit external to the substrate, by a driver circuit formed on the same substrate as the pixel.
This type of active matrix display device has been in the spotlight because of the many advantage which can be obtained by incorporating various circuits and elements on the same substrate in this type of active matrix display device, such as reduced manufacturing cost, small size, increased yield, and higher throughput.
An EL layer (light emitting layer) is made to emit light in an active matrix EL display device by disposing a switching element formed from a TFT to each pixel, and by driving a driver element that performs current control by the switching element. For example, there are EL display devices disclosed in U.S. Pat. No. 5,684,365 (Japanese Patent Application Laid-Open No. Hei 8-234683) and Japanese Patent Application Laid-Open No. Hei 10-189252.
Degradation of EL materials due to moisture has been a problem in these EL display devices. Specifically organic EL materials degrade not only by moisture but also by oxygen. Accordingly EL elements are generally shielded from moisture, etc., by sealing the EL elements as disclosed in Japanese Patent Application Laid-Open No. Hei 8-78159.
However, the problem that the EL layer has is not limited to moisture. The EL layer includes alkaline metals such as sodium (Na) in itself, and a serious trouble can be caused to the operation of TFTs when the alkali metals are diffused into the TFTS. Further, degradation due to storage of heat is also a problem because an EL layer is weak to heat. Note that alkaline metals are referred to xe2x80x98alkaline metalsxe2x80x99 to include alkali earth metals through the Specification.
In view of the above conventional technique, an object of the present invention is to provide an electro-optical device having good operation performance and high reliability, and in particular, to provide an EL display device. Another object of the present invention is to increase the quality of electronic equipment (an electronic device) having the electro-optical device as a display by increasing the image quality of the electro-optical device.
In order to achieve the above objects, degradation of EL elements due to moisture, degradation due to heat and release of alkaline metals are prevented in the present invention. In concrete, an insulating film which satisfies these is disposed in contact with the EL elements, or more preferably the EL elements are enclosed by such insulating films.
Namely, an insulating film, which has a blocking effect of moisture and alkaline metals, and a heat radiating effect is disposed to a nearest position to the EL elements, and degradation of the El elements is suppressed by the insulating film. Note that a laminate of an insulating film having blocking effect against moisture and alkaline metals and an insulating film having heat radiating effect can be used in case that such insulating film cannot be used by a single layer. Further, it is possible to use laminate of an insulating film having blocking effect against moisture, an insulating film having blocking effect against alkaline metals and an insulating film having heat radiating effect.
In either way, measures against both of moisture and heat should be sought in order to suppress degradation of the EL layer (it may also be referred to as degradation of EL element), and it is necessary to take measures against heat, moisture and alkaline metals for the TFTs themselves that driver the EL elements.